Emergency lighting circuit

ABSTRACT

In an emergency lighting circuit, a relay is provided with its coil in parallel with a capacitor in the mercury lamp circuit. Normally closed contacts of the relay are connected in series between a power supply and an incandescent lamp, in order to energize the incandescent lamp whenever the mercury lamp is deenergized.

United States Patent Inventor Jack E. llaymaker Newark, Ohio Appl. No. 838,185

Filed July 1, 1969 Patented Aug. 10, 1971 Assignee Holophme Company, Inc.

New York, N.Y.

EMERGENCY LIGHTING CIRCUIT 7 Claims, 4 Drawing Figs.

US. Cl. 315/93, 315/92, 315/136 Int. Cl ..l-l05b 39/10, HOSb 41/46 Field of Search 315/88, 89,

References Cited UNITED STATES PATENTS 3,517,254 6/1970 McNamara. Jr 315/93 X FOREIGN PATENTS 377,937 7/1964 Switzerland 315/92 Primary Examiner-Raymond F. l-lossfeld Attorney-Nolte and Nolte ABSTRACT: In an emergency lighting circuit, a relay is provided with its coil in parallel with a capacitor in the mercury lamp circuit. Normally closed contacts of the relay are connected in series between a power supply and an incandescent lamp, in order to energize the incandescent lamp whenever the mercury lamp is deenergized.

MEACl/HYMMP EMERGENCY LIGHTING CIRCUIT This invention relates to an emergency lighting circuit, and more in particular to a circuit for energizing an incandescent lamp to provide emergency lighting in the event of interruption of power to a mercury lamp.

One of the problems which occurs in the use of mercury lamps, such as mercury vapor discharge lamps, resides in the fact that, upon interruption of power for a few cycles, the mercury lamp will become extinguished, and relighting of the lamp will not occur immediately on restoration of the power source. For example, it may require to minutes for the mercury lamp to cool sufficiently for the lamp to restrike. In such cases, it may be desirable or necessary to provide an emergency or auxiliary lighting circuit in order to provide illumination during the off period of the mercury lamp. While circuits have been suggested in the past for providing such emergency illumination, in response to off periods of the mercury lamp, such circuits have in general been relatively complicated and expensive, and have employed many components.

In one example of a circuit which has been suggested for providing emergency illumination, a relay is provided with its coil in series with the discharge lamp, the contacts of the relay being connected to energize an incandescent lamp. It has been found, however, that this arrangement introduces a number of problems. Such a system requires a current-sensing relay, and the DC resistance and AC impedance of the relay coil directly affect the lamp current. The DC resistance and AC impedance of the relay coil must therefore be very low, for example, having a total of 2 ohms, in order not to have an adverse effect on the mercury discharge lamp wattage. In addition, if the impedance of the relay coil is too high, a special ballast must be designed to compensate for the relay coil impedance. Consequently, the coil for a current relay for such an application must be wound with only a few turns of wire, so that a different current-sensing relay must be designed for each specific combination of a relay and ballast lamp. Furthermore, it has been found that, since such a relay coil has only a few turns, the current adjustment of the coil is critical. An additional disadvantage of such an emergency lighting circuit, the operation of the current relay is dependent upon the lamp current, so that different relays must be employed for application with discharge lamps of different ratings. For example, a relay designed to operate in a circuit for a 400-watt lamp drawing 3.2 amperes would not operate reliably when used with a 100- watt lamp circuit drawing 0.9 amperes. Conversely, a relay designed to operate in a lamp circuit at 0.9 amperes would overheat if it were to be used in a circuit drawing 3.2 amperes.

It is therefore an object of this invention to provide an emergency lighting circuit for a discharge lamp, in which a noncritical relay may be employed that does not adversely affect the current in the circuit or require the use of a specially designed ballast, and wherein a relay may be employed in combination with discharge lamps having substantially different ratings.

According to the present invention, this problem is obviated by providing an emergency lighting circuit which includes a relay having its energizing coil connected in parallel with the capacitor in the mercury lamp circuit. The relay has a set of normally closed contacts which are connected between an incandescent lamp and a power source, which may be the same power source as that employed for the mercury lamp, so that the incandescent lamp will be energized whenever the mercury lamp is extinguished.

The invention will now be described in more detail with reference to the accompanying drawings in which:

FIG. 1 is a circuit diagram of an emergency lighting circuit according to one embodiment of the invention,

FIG. 2 is a circuit diagram of a modification of the circuit of FIG. 1,

FIG. 3 is a circuit diagram of a further modification of the circuit of FIG. 1, in which a transformer having an isolated primary and secondary winding ballast is substituted for the autotransformer and ballast of the circuit of FIG. 1, and

FIG. 4 is a circuit diagram of still another modification of the circuit of FIG. 1, in which the relay is energized by way of a control transformer.

Referring now to FIG. 1, an alternating supply voltage at terminals 10 and 1 1 is applied to the primary winding of an autotransformer 12. A mercury lamp 13 is energized from the secondary of the autotransformer 12 by way of a ballast circuit comprising series-connected capacitor 14 and inductive reactor 15. This portion of the circuit is conventional, and alternatively many obvious modifications in the energization circuit of the mercury lamp may be employed without departing from the scope of the present invention.

A relay 20 is provided having its energizing coil 21 connected in a parallel with the capacitor 14. The relay 20 has a set of normally closed contacts 22 which are connected in series with the incandescent lamp 23 between the terminals 10 and 11.

In operation, when the mercury lamp is energized, the voltage on the capacitor'causes current to flow through the relay winding 21, so that the contacts 22 are reopened and the incandescent lamp 23 is deenergized. In the event of a momentary power failure of the power supply at terminals 10 and 11, the mercury lamp 13 will become extinguished, and restriking of the lamp may be from 10 to 15 minutes. During this delay period, there is no voltage across the capacitor and no current flows through the relay coil 21 to hold the contacts 22 in their open position, and consequently the relay becomes deenergized and the lamp 23 will be connected to the terminals 10 and 1 l by way of contacts 22. The consequent energization of the lamp 23 continues until the arc is restruck in the mercury lamp 13, at which time the contacts 22 once again open to effect the extinguishing of the incandescent lamp 23.

In the arrangement of FIG. 1, the relay is a voltage-sensing relay, and consequently has a relatively high DC resistance and AC impedance. The current required to energize the relay is therefore relatively low, and does not adversely affect the lamp current, so that it has a negligible efiect on the ballast adjustment. Although some of the lamp current will or course flow through the relay winding, the impedance of this winding is high in comparison with the impedance of the capacitor 14, so that energization of the relay will essentially be a function of the potential developed across the capacitor 14. Since the relay winding 21 has a relatively high DC resistance and AC impedance, it may be wound from a large number of turns, and consequently, the adjustment of this relay is not critical. In addition, the energization of the relay 20 is substantially unaffected by differences in lamp current, and may consequently be employed in circuits employing mercury discharge lamps of substantially different wattage readings. As an example, a -watt mercury discharge lamp has a lamp current of approximately 0.9 amperes, and a 400-watt mercu ry discharge lamp has a lamp current of approximately 3.2 amperes. The capacitor voltage for both lamps, however, is approximately the same, so that the same relay operates equally well in both lamp circuits. In one example of the circuit of FIG. 1, a General Electric mode No. 3ARR4-19ac relay, having a DC coil resistance of approximately 5,700 ohm, and AC impedance of approximately 7,000 ohms and an inductance of about 10 h. was employed for the relay 20. The current required for energization of the relay in one circuit was less than 50 milliamperes so that when the relay was placed across the capacitor in the secondary circuit of the mercury lamp ballast, it had negligible effect on the ballast adjustment. In this embodiment the capacitor 14 may have a capacitance of 35 mf., with a reactance of about 75 ohms, and the total ballast impedance may be about 75 ohms.

In the embodiment of the invention illustrated in FIG. 2, instead of being connected to the terminals 10 and 11 as in the arrangement of FIG. 1, the incandescent lamp 23 is connected by way of the contacts 22 to terminals 25 and 26. The terminals 25 and 26 are adapted to be connected to a power supply separate from the power supply connected to the terminals 10 and 11. The arrangement of FIG. 2 operates in the same manner as the arrangement of FIG. 1, with the exception that the illumination of the incandescent lamp 23 is no longer dependent upon the power supply connected to the terminals and 11, so that the lamp 23 may be energized during conditions of absence of current flow in the mercury lamp 13 even during extended periods of failure of the supply connected to the terminals 10 and 11.

Referring now to FIG. 3, therein is illustrated a modification of the circuit of FIG. 1, in which the autotransformer 12 has been replaced by a transformer 30 having a primary winding 31 connected between the terminals 10 and 11, and an isolated secondary winding 32. The secondary winding 32 is connected in series with the capacitor 14 and mercury lamp l3, and the winding 32 is designed so that no additional ballast inductance is required. This arrangement operates as well as the circuit of F IG. 1, and does not require a separate ballast windmg.

In the arrangement of FIG. 4, which illustrates another modification of the circuit of FIG. 1, the coil 21 of relay 20, instead of being connected directly across the capacitor 14, is connected to the secondary winding 35 of a control transformer 36. The primary winding 37 of the control transformer is connected in parallel with the capacitor 14. This arrangement is particularly suitable when it is desired to employ a standard relay for the relay 20, having a voltage rating less than the voltage normally developed across the capacitor 14. In this event, the control transformer 36 is employed to step down the voltage across the capacitor 36 to a voltage suitable for operation of the relay 20.

While the invention has been particularly described with reference to mercury vapor discharge lamps, it is obvious that the invention has application in combination with other types of lamps which require delay periods before reignition following a power failure. Similarly, it will be readily apparent that the relay coil 21 may be connected in parallel with other components in the energizing circuit of the mercury lamp 13, so that the coil is responsive to the voltage drop created by the current flow in the mercury lamp for energizing and deenergizing the incandescent lamp.

As a further modification of the arrangement of FIGS. 1 through 4, it is apparent that each of these circuits may employ a time delay relay for the relay 2]. By employing a time delay relay, the extinguishing of the incandescent lamps is delayed until after the mercury restrikes. This delay may be advantageous, in order that the incandescent lamp remain lit until the mercury lamp has reached its full brightness, in order to maintain a high level of illumination at all times.

What I claim is:

1. In a gas discharge lamplighting circuit of the type comprising a gas discharge lamp, a source of energizing power for said lamp, and ballast circuit means for energizing said gas discharge lamp form said source, and wherein said ballast circuit means includes at least one reactance means having a voltage thereacross dependent upon the current through said gas discharge lamp, the improvement comprising an incandescent lamp, relay means having an energizing coil and normally closed contact means, means connecting said coil in parallel with said reactance means, the DC resistance and AC impedance of said coil being high with respect to the impedance of said reactance means, and means for energizing said incandescent lamp by way of said normally closed contact means, whereby said incandescent lamp is energized when said gas discharge lamp is extinguished.

2. The circuit of claim 1 wherein said source of power comprises first and second terminals, and said means for energizing an incandescent lamp comprises means connecting said incandescent lamp to said first and second terminals by way of said normally closed contacts.

3. The circuit of claim 1 wherein said means for energizing said incandescent lamp comprises a second source of power independent of said first source, and means connecting said incandescent lamp to said second source of power by way of said normally closed contact means.

4. The circuit of claim 1 wherein said reactance means comprises a capacitor connected in series with said gas discharge lamp and said relay coil is connected in parallel with said capacitor.

5. The circuit of claim 4 wherein said ballast circuit means further comprises an inductive means serially connected with said gas discharge lamp, and wherein said circuit further comprises autotransformer means connected between said source of power and said ballast circuit means.

6. The circuit of claim 1 wherein said means connecting said coil in parallel with said reactance means comprises a transformer having a primary winding connected in parallel with said reactance means, and a secondary winding connected to said coil.

7. The circuit of claim 1 wherein said ballast circuit means for energizing the gas discharge lamp from said source comprises a transformer having a primary winding connected to said source, and an isolated secondary winding connected in series with said gas discharge lamp and said reactance means. 

1. In a gas discharge lamplighting circuit of the type comprising a gas discharge lamp, a source of energizing power for said lamp, and ballast circuit means for energizing said gas discharge lamp form said source, and wherein said ballast circuit means includes at least one reactance means having a voltage thereacross dependent upon the current through said gas discharge lamp, the improvement comprising an incandescent lamp, relay means having an energizing coil and normally closed contact means, means connecting said coil in parallel with said reactance means, the DC resistance and AC impedance of said coil being high with respect to the impedance of said reactance means, and means for energizing said incandescent lamp by way of said normally closed contact means, whereby said incandescent lamp is energized when said gas discharge lamp is extinguished.
 2. The circuit of claim 1 wherein said source of power comprises first and second terminals, and said means for energizing an incandescent lamp comprises means connecting said incandescent lamp to said first and second terminals by way of said normally closed contacts.
 3. The circuit of claim 1 wherein said means for energizing said incandescent lamp comprises a second source of power independent of said first source, and means connecting said incandescent lamp to said second source of power by way of said normally closed contact means.
 4. The circuit of claim 1 wherein said reactance means comprises a capacitor connected in series with said gas discharge lamp and said relay coil is connected in parallel with said capacitor.
 5. The circuit of claim 4 wherein said ballast circuit means further comprises an inductive means serially connected with said gas discharge lamp, and wherein said circuit further comprises autotransformer means connected between said source of power and said ballast circuit means.
 6. The circuit of claim 1 wherein said means connecting said coil in parallel with said reactance means comprises a transformer having a primary winding connected in parallel with said reactance means, and a secondary winding connected to said coil.
 7. The circuit of claim 1 wherein said ballast circuit means for energizing the gas discharge lamp from said source comprises a transformer having a primary winding connected to said source, and an isolated secondary winding connected in series with said gas discharge lamp and said reactance means. 